southern australia seasonal bushfire ......overview the seasonal bushfire outlook for southern...
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OVERVIEW
The Seasonal Bushfire Outlook for southern Australia is used by fire authorities to make strategic decisions on resource planning and prescribed fire management for the upcoming fire season. The outlook is developed at an annual workshop convened by the Bushfire and Natural Hazards CRC and the Australasian Fire and Emergency Service Authorities Council (AFAC).
At the 2016 workshop in Brisbane in August, the Outlook was assessed and a range of broad climate factors were considered.
The above map shows the bushfire
outlook for southern Australia through
to the end of 2016. This map has been
combined with the outlook for the
northern Australia bushfire season, which
was released at the beginning of July, to
show the areas of fire potential for all of
Australia. (See Hazard Note 18, July 2016).
This Outlook will be reviewed towards
the end of spring to take into account
the impacts of actual temperatures and
rainfall in the lead up to summer.
The Southern Seasonal Bushfire
Assessment Workshop brought together
fire and land managers, climatologists and
meteorologists to evaluate the upcoming
season for the southern part of Australia.
BUSHFIRE POTENTIAL
Fire season potential depends on several
factors. The amount, location and timing
of rainfall in the period leading up to
the fire season are critically important
for estimating fuel loads and dryness.
The temperature and rainfall outlooks for
the next few months are crucial factors for
influencing the development of fire threat.
Above Normal Normal Below Normal
Bushfire Potential 2016
SOUTHERN AUSTRALIA SEASONAL BUSHFIRE OUTLOOK 2016
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ISSUE 019 AUGUST 2016TOPICS IN THIS EDITION | FIRE WEATHER | FUEL MANAGEMENT
Of particular importance are the future
tendencies of sea surface temperatures in the
Pacific Ocean, associated with the El Niño-
Southern Oscillation, and those in the Indian
Ocean. These are major drivers of climate over
much of Australia. Other factors considered
include the distribution of firefighting
resources to meet potential threats, as well
as previous fire activity and the amount of
prescribed burning that can reduce the threat.
The workshop discussed the weather,
landscape conditions and cross-border
implications leading into summer and
determined areas that had the potential
for a fire season that was above normal,
normal or below normal. Attendees
included representatives of the Bushfire and
Natural Hazards CRC, AFAC, the Bureau
of Meteorology, Queensland Fire and
Emergency Services, Tasmania Fire Service,
the Australian Capital Territory Emergency
Service Agency, the New South Wales Rural
Fire Service, South Australia’s Country Fire
Service, Victoria’s Country Fire Authority
and Department of Environment Land,
Water and Planning, and Western Australia’s
Department of Parks and Wildlife and the
Department of Fire and Emergency Services.
ANTECEDENT CONDITIONS
For every month of 2016 the Australian national
mean temperature has been above average.
This warmth culminated in the August 2015
to July 2016 period was +1.33 °C above the
1961-1990 average, the largest anomaly for any
12-month period since records began in 1910.
Despite a number of significant cold
spells, winter has continued the pattern
of above average temperatures, with a
mean temperature anomaly of +0.9˚C
(Figure 1). The longer term changes are
important for the season ahead, noting that
summer 2015/2016 marked the fourteenth
consecutive warmer than average southern
fire season (October to April). These warmer
conditions have contributed to elevated
fire risk in most years in recent decades.
After a dry second half of 2015, most
parts of Australia have seen very good
rainfall since mid-autumn 2016 (Figure 2).
Nationwide, preliminary analysis shows that
winter 2016 saw a national average rainfall of
116mm, the second wettest on record. June
and July were both particularly wet months,
with June 2016 being the second-wettest
June on record, while large areas of the
country reported record high rainfall during
July. The pattern of heavy rainfall following a
strong El Niño is not uncommon and is tied to
the warming of ocean waters around Australia.
Winter rainfall was particularly good across
Queensland, most of NSW, Tasmania, eastern
Victoria and parts of inland and central
districts of South Australia and eastern
Western Australia. A beneficial result of the
above average rainfall has been the removal
of short-term rainfall deficiencies, with soil
moisture now near or above normal. Rainfall
tended closer to average in remaining
parts of Victoria and the west coast and
Murray Mallee areas of South Australia.
The far south west of Western Australia
has experienced another winter of below
average rainfall, meaning that 15 of the past
16 winters have been below average. In this
region the long-term drying of vegetation
and the landscape continues in a pattern
that became established in the 1970s.
The generally good rainfall and above
average temperatures has seen vegetation
growth that is above average across
much of southern and eastern Australia,
particularly through much of New South
Wales. With good soil moisture conditions
and above average rainfall forecast, this
pattern is expected to continue for
some months, increasing fuel loads.
Winter 2016 was a period that saw Australia’s
climate become strongly influenced by a
negative Indian Ocean Dipole. This pattern
tends to increase winter and spring rainfall for
southern and eastern Australia and generally
sees cooler than average temperatures. Typically,
once a negative Indian Ocean Dipole becomes
established in the winter, it is expected to
persist through spring and decay rapidly in
summer. Meanwhile, ocean temperatures along
the equatorial Pacific returned to near average
values following the end of the strong 2015/16
El Niño. The range of observations and model
forecasts suggest that the tropical Pacific
will continue to remain in neutral conditions
(though just falling short of a La Niña) or may
see the development of a weak La Niña. The
Indian Ocean Dipole is expected to persist into
spring, and is likely to end around November.
CLIMATE OUTLOOK
The climate outlook for the coming three
months is influenced by both the Pacific
and Indian Oceans. The combination
of neutral to near La Niña in the Pacific
and a negative Indian Ocean Dipole
favours wetter than average conditions
in many areas. While the natural drivers
will tend to reduce temperatures, the
overall pattern of well above average
global temperatures (i.e., global warming)
means that Australian temperatures are
expected to be mostly above average.
The outlook for spring rainfall indicates
a higher chance of above average rainfall
is likely across most of northern and
eastern Australia. The probability of above
average is typically in the range of 55 to
65 percent, meaning a leaning towards
wetter than average conditions. In some
contrast, the odds in south west Australia are
tending towards below average rainfall. The
rainfall odds are close to 50:50 elsewhere.
FIGURE 1 FIGURE 2
2
The outlook for both maximum and
minimum temperatures strongly favours
above average temperatures across most of
Australia. The likelihood of above average
temperatures is typically in the range of 60
to 75 per cent, locally exceeding 80 per cent
in Tasmania and in some northern areas. This
forecast suggests that Australia is likely to
experience another warmer than average
spring, with summer-like temperatures
likely to start earlier in southern
Australia than is historically the case.
Updates to forecasts and the outlook for
the Indian Ocean Dipole and La Niña are
published at www.bom.gov.au/climate/ahead.
REGIONAL SUMMARIES
QUEENSLANDWhile some parts of inland Queensland
have seen record rainfalls, much of the state
remains drought affected and grass fuel loads
are still sparse to moderate in these areas.
With the exception of the south east
corner of the state, forested areas have
received above average rainfall in the three
months leading up to the start of the fire
season. As a result the fire season is likely
to see a slower start than usual. The outlook
is for lower maximum temperatures and
above average rainfall through to October.
These two factors, plus the likelihood of
an early northern rainfall onset, make the
potential of an above normal fire season
unlikely across most of Queensland.
Queensland Fire and Emergency Services
worked closely with Queensland Parks and
Wildlife around Rockhampton to assess
the increased risk as a result of Severe
Tropical Cyclone Marcia in preparation
for the 2015 fire season. Mitigation
activities guided by these assessments
continued in the lead up to the 2016
season. Residual risk remains in the area
and this will be a focus again this season.
Soil moisture is relatively dry to the
west of the Great Dividing Range, from
around Bundaberg, and south to the New
South Wales border, particularly around
Biggenden, Gayndah, Kingaroy and Dalby.
While normal fire potential is expected
for this outlook period, it is important
to recognise that an active fire season
is still probable and more likely in the
areas with the underlying soil dryness.
NEW SOUTH WALESA delayed start to the bushfire season in
New South Wales is likely due to above
average winter rainfall for much of the state,
and a prediction for the chance of above
average rainfall over the next three months.
However, a predicted end to the current
negative Indian Ocean Dipole and more
neutral El Niño-Southern Oscillation
conditions in spring could see a shift
away from wetter and cooler conditions
towards more typical summer conditions.
This shift could be exacerbated by the
warmer than average temperatures –
as part of a global warming trend –
that are drying forest and grassland fuels.
It is expected that the significantly higher
than average rainfall received over winter in
the central and western parts of the state
will result in prolific grass growth over spring.
This grass growth, combined with a drying
phase and summer conditions, could lead to
above normal fire potential for central and
western grassland areas during summer.
The trend towards significantly
exceeding average rainfall totals was less
pronounced adjacent to the south western
and western boundaries of the state. As a
result, the prediction here is for normal
bushfire potential as the likelihood of
prolific growth is not considered high.
The Sydney Basin and the Greater Hunter
have followed the trend for above average
rainfall over winter and are likely to see
a delayed start to the bushfire season.
However, the prediction for conditions to
shift towards more typical conditions over
summer could see fuel availability coinciding
with the peak of summer, leading to the
prediction for normal bushfire potential.
Forested areas south of Sydney have also
received above average rainfall over winter.
A late start to the fire season is common for
these areas and, therefore, fire potential is
expected to follow a normal season pattern.
Recent rainfall in northern New
South Wales has reduced the potential
from the early predictions of an above
normal season, to a season that is likely
to follow a more normal pattern.
ACT After three wet months the upper soils in the
Australian Capital Territory are wetter than
average for this time of year. The forecast
changes of the Pacific and Indian Oceans,
towards climatically neutral conditions, are
expected to bring near average rainfalls and
temperatures through to at least November.
This could encourage an early and vigorous
growth of grasses. It will also boost the
recovery of the high country forests that
have been affected by large fires since 2003.
These higher fuel loads may be offset by
the effects of rainfall on fuel flammability.
High levels of grassland curing may
not be seen until mid-summer at the
earliest. The amount of flammable fine
fuels in the forest areas is also expected
to remain low until mid-summer.
As a result, the bushfire potential for this
outlook period is assessed as normal.
As summer approaches, conditions
will be closely monitored, particularly
if there is an earlier than currently
expected change to drier conditions.
VICTORIA East Gippsland has a mostly below normal
fire potential this year. It has received very
much above average rain in the short and
long term, and the temperature outlook is not
likely to support strong late spring drying in
the forests. The fire season in East Gippsland
is expected to begin later than normal on
these current signals. The marginal chances
of above average rain along the Murray
River and in Far East Gippsland raise the
possibility of a delayed start to the fire season
in those areas. This also means the Murray
FIGURE 3
3
Valley is likely to have normal fire potential
despite underlying dryness in some areas.
In west and south Gippsland, parts of
Victoria’s Central Highlands, including
Melbourne’s water catchments, and across
most of south west Victoria, the slight
chance of above average rain coupled with a
high probably (80 percent) of above average
temperatures, plus existing severe rainfall
deficits, indicates strong late spring drying is
likely in forested areas. This could see rapidly
escalating fire behaviour later in summer.
Most soils in the extensive western grass
plains and their forests have saturated upper
layers this year, in many areas evidenced by
accumulations of surface water; but a dryness
remains at deeper levels, and the current
weak signal for spring rain is likely to mean
good overall grass growth in these areas, with
insufficient available water to soak deeper into
the soil to reduce the fire risk in the forests.
Melbourne’s water catchments have not yet
been saturated and now have a long history of
underlying dryness. Forest fuels have increased
since the 2009 fires, so there is once again
potential for fire. Similarly, the eastern Otway
Range, Brisbane Ranges, Wombat Forest, and
drier forest types bordering Victoria’s box
ironbark belt also have a long history of dryness.
These areas have above normal fire potential.
TASMANIAThe start of the fire season in Tasmania
will be delayed as long as top up
rains continue, which is expected to
at least October and possibly later.
Fuels less influenced by soil moisture
such as moorlands, heaths and scrubs,
have a normal bushfire potential, while
forest fuels have normal to below normal
bushfire potential. Grassland fuels have
a normal to below normal potential, but
will provide a significant threat in the
New Year when they are cured. Given
the wet outlook for the next few months,
opportunities for planned burning will
be very limited, at least until autumn.
By early summer, without top up rain,
most fuels will have a normal potential
in terms of ignitability. Fire weather
conditions are likely to be average or even
subdued. However, if rainfall is above
moisture availability, pasture biomass,
recent bushfire and prescribed burning
history and forecasted weather conditions.
In the Eastern Gascoyne, Murchison,
Goldfields, Central West and Desert areas,
there is normal bushfire potential due
to average rainfall and grass growth.
In the Western Gascoyne and Pilbara
regions there is above normal fire
potential as a consequence of higher
than average grass fuel loads in response
to above average soil moisture.
The Wheatbelt and Great Southern
regions have above average grass
fuel loads for this time of the year
due to good rainfall. However, this
is not expected to result in above
average fuel loads at the end of the
growing season, given the impacts
of crop harvesting and grazing.
In the Eucla, east of Norseman,
above average soil moisture and
subsequent pasture growth, combined
with pre-existing mature fuels, have
resulted in the expectation of higher
than normal bushfire potential.
In the South West, despite early and close
to average rainfall, there is an underlying
long-term deficit in the soil moisture.
Recent bushfires and prescribed burning
have reduced fuel loads in localised areas.
However, on the landscape scale, the
current high loads of forest fuels have
resulted in above normal fire potential.
average the fire season potential will
be below normal at least until the New
Year, when grasslands will cure. Overall,
the state has normal bushfire potential.
SOUTH AUSTRALIASouth Australia has experienced a wetter
than average winter, resulting in the current
Soil Dryness Index being below the 10-year
average across the state. The potential
for slightly above average rain is forecast
to continue through September and
into October, which may lead to the fire
season starting later than in recent years.
This puts the outlook in line with
the more traditional South Australian fire
season, and as a result, current indications
are that most parts of the state can
expect a normal fire season. Good rainfall
will promote growth, particularly in pastoral
areas; however, many of the forested
areas have received good soaking rains
and will not burn as early as they have in
previous years. The exception is parts of
the Mallee and Upper South East of the
state, which have experienced significant
rainfall deficits in recent years. As a result,
and despite recent rainfall, these areas are
assessed as above normal fire potential.
WESTERN AUSTRALIAThe bushfire outlook for Western Australia
has been derived from several information
sources including the relative root zone
FIGURE 4
The Bushfire and Natural Hazards CRC is a national research centre funded by the Australian Government Cooperative Research Centre Program. It was formed in 2013 for an eight-year program to undertake end-user focused research for Australia and New Zealand.
Hazard Notes are prepared from available research
at the time of publication to encourage discussion
and debate. The contents of Hazard Notes do not
necessarily represent the views, policies, practices
or positions of any of the individual agencies or
organisations who are stakeholders of the Bushfire
and Natural Hazards CRC.
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